\documentclass[12pt]{article}   
 \textheight15cm \textwidth11cm \parindent0mm \parskip 1ex plus2ex minus0.8ex
\begin{document}
\newcounter{flno}
\newcommand{\apartment}[1]{\stepcounter{flno}Apartment No.\ \arabic{flno}: #1\par}
 \apartment{blue apartment}
 \apartment{velvet apartment}
 \apartment{president suite}

\renewcommand{\thesubsection}{\arabic{section}-\alph{subsection}}
\section{A Section starts}
\subsection{A Subsection starts}
\end{document}
